Conventionally, a rotary actuator used in, for example, a drive portion of a shift-by-wire system is known. A rotary actuator disclosed in Patent Document 1 (Japanese Patent No. 4560743 corresponding to US 2009/0189468) includes a speed reduction portion having an internal gear and an external gear. The internal gear is press-fitted to an inner wall of an annular plate provided in a resin housing. Protrusions provided integrally with an outer wall of the internal gear are inserted into recesses of an inner wall of the housing. The housing has an attachment holes located at positions same as positions of the recesses in a circumferential direction of the housing.
In the rotary actuator disclosed in Patent Document 1, the recesses and the attachment holes both of which can cause stress concentration are same as each other in position in the circumferential direction. Thus, stress applied on the housing in the press-fitting of the internal gear concentrates on parts of the housing where the recesses and the attachment holes are located. Therefore, cracking may be generated at the parts of the housing where the recesses and the attachment holes are located. Moreover, if the cracking further extends, the housing may be broken.